The Occupational Safety and Health Administration is investigating a fire at a Jamestown, Pa. munitions manufacturing plant for the second time in the last five months.

OSHA currently has three open investigations at Combined Systems Inc. on Kinsman Road, including the early Tuesday fire that caused 12 employees to be taken to UPMC Horizon Hospital in Greenville with breathing problems.

Four ambulances were called to the plant after the fire ignited at about 5:45 a.m.

Jamestown Fire Chief Mike Cadman said the fire ignited in the part of the building where gas canisters are made. The small fire was quickly extinguished by a newly installed sprinkler system, Cadman said.

“One of the main safety guys out there is a fellow fire chief. They take safety pretty high out there as a company,” said Cadman.

The dozen employees inhaled a non-lethal gas that causes irritation when exposed to skin or inhaled, Cadman said. Some employees experienced wheezing, coughing and other pulmonary problems and were taken UPMC Horizon hospital for treatment.

“The symptoms usually go away with exposure to high flow oxygen or de-exposure to the irritant, meaning getting them out of the way where the exposure was or where the smoke was,” said Dr. Joseph Noga, UPMC Horizon.

The rest of the building sustained moderate heat damage.

It’s the fourth fire at the company since Nov. 15, 2011, when a fire destroyed a building on the company’s property.

OSHA has issued 24 serious citations against the company since 2007, paying $32,680 in fines, including $18,720 in fines for six safety violations in 2009.

The company, with about 170 employees, manufactures tactical munitions and crowd control devices, like tear gas, for law enforcement, corrections and homeland security agencies, according to its website.

A message left at the company has not yet been returned.

The last fire at the plant, on April 22, sent one employee to an area hospital via emergency helicopter after an explosion and fire. A cause of that fire has not yet been determined and is currently being investigated by OSHA.

Nearby residents expressed concerns after that fire.

OSHA records say that in Feb. 20, 2012, an explosion caused extensive damage to the building but no employee sustained injuries.